Indicating and actuating fuses



April 20, 1965 K. w. SWAIN 3,179,774

INDIGATING AND ACTUATING FUSES Filed Aug. 21. 1961 lzwezzfofl: KezarzebwWswaim United States Patent 3,179,774 INDICATING AND ACTUATING FUSESKenneth W. Swain, Hampton Falls, N.H., assignor to The Chase ShawmutCompany, Newburyport, Mass. Filed Aug. 21, 1961, Ser. No. 135,696

4 Claims. (Cl. 200-121) This invention relates to electric indicatingand actuating fuses.

It is a general object of this invention to provide improved electricfuses of the above description, or type.

Another object of this invention is to provide indicating and actuatingfuses which are normally not intended to carry electric currents and areintended to blow when, due to an abnormal condition, they are caused tocarry electric currents. Such indicating and'actuating fuses aregenerally shunted across power or main fuses normally carrying electriccurrents, and the former fuses blow in response to blowing of thelatter. When blowing, the former fuses indicate the blowing of the poweror main fuses which they are shunting, or the former fuses cause someactuation in response to blowing of the power or main fuses.

It is another object of the invention to provide improved indicating andactuating fuses which are particularly adapted to be arranged at pointsremote from the power or main fuses and lend themselves well to performeither a visual indicating function, or a mechanical operating duty, orany electrical switching duty, as called for by any particular set ofcircumstances.

Another object of the invention is to provide improved indicating andactuating fuses which are highly flexible or adaptable, i.e. which lendthemselves to be adapted by small changes to a number of different, orspecialized, applications.

Other objects of the invention are to provide improved indicating andactuating fuses designed to preclude hot products of arcing fromescaping from the casings of the fuses and to preclude outer corrosiveatmospheres from penetrating into the casings of the fuses, and tothereby damage the fusible restraining wires arranged inside of thecasings thereof.

Another object of the invention is to provide improved indicating andactuating fuses which combine a strong mechanical tie between thespring-biased striker pin and the restraining wire for the striker pinwith gas-tightness.

A further object of this invention is to provide improved indicating andactuating fuses having casings of insulating materials different fromthose of prior art fuses.

U.S. Patent 2,794,095 to Frederick J. Kozacka, May 28, 1957, Striker PinStructures discloses an electric indicating and actuating fuse whereinthe restraining wire for the striker pin is soldered to the latter. Suchsolder connections are not of a permanent nature, i.e. they graduallygive by virtue of cold flow of the solder under the continued action ofthe spring bias to which the striker pin is normally subjected.

It is, therefore, another object of this invention to provide improvedindicating and actuating fuses which are not subject to theaforementioned limitation.

U.S. Patent 2,914,636 to Frederick J. Kozacka, Nov. 24, 1959,Miniaturized High Current-Carrying Capacity Current-Limiting Fuses WithBuilt-In Indicating Plungers, and U.S. Patent 2,918,551 to Frederick J.Kozacka, Dec 22, 1959, Fuses With Built-In Indicating Plungers, discloseindicating and actuating fuses wherein the connection between thestriker pin and the restraining wire for the latter is of a permanentnature. These fuses call for a looped restraining wire doubling thelength thereof, and therefore it is necessary to provide in such fuses ahighly effective de-ionizer, or arc-quenching filler such as, forinstance, quartz sand. The provision of such a 3,17%,774 Patented Apr.20,1965

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filler requires, in turn, the provision of relatively expensive casingscapable of containing the hot fulgurite resulting from fusion of thetiller on blowing of the fuse.

It is, therefore, another object of this invention to procide improvedindicating and actuating fuses which are not subject to theaforementioned limitations.

U.S. Patents 2,794,096 to Frederick J. Kozacka, May 28, 1957, HighInterrupting Capacity Current-Limiting Fuses With Striker Pins, and U.S.Patent 2,834,852 to Kenneth W. Swain et al., Plug-In Type Power Fuses,disclose main or power fuses including integrated indicating andactuating fuses whose striker-pin-restraining-wires shunt theribbon-type fuse links of the main or power fuse. The striker pin is inthe shape of a rugged plunger adapted to perform a relatively onerousmechanical duty, particularly that of tripping a circuit breaker. Astriker pin intended to perform a switching operation rather than toperform a mechanical duty should preferably be silverplated. The kind ofstriker pins shown in the above U.S. patents do not lend themselves tosilver plating because they are provided with narrow passages forreceiving the restraining wire which passages tend to retain highlycorrosive plating liquids. Another limitation of the structuresdisclosed in the above patents consists in that the knotted ends of therestraining wires are exposed to the outer atmosphere which may bedamaging if the latter is corrosive. Restraining wires are generallymade of steel because they require a high tensile-strength, and maylllllst and be impaired if exposed to a humid or damp atmosp ere.

It is, therefore, another object of the invention to provide indicatingand actuating fuses which are not subject to the aforementionedlimitations.

The foregoing and other general and special objects of the invention andadvantages thereof will more clearly appear from the ensuing particulardescription of the invention, as illustrated in the accompanying drawingwherein:

FIG. 1 is a longitudinal section of an indicating and actuating fuseembodying the invention;

FIG. 2 is a section taken along 22 of FIG. 1;

FIG. 3 is an end view of the striker pin mechanism;

FIG. 4 shows in longitudinal section a modified detail of the structureof FIG. 1, and

FIG. 5 shows in longitudinal section another modified detail of thestructure of FIG. 1.

Referring now to the drawing, numeral 1 has been applied to indicate atubular casing of insulating material. As a general rule casings ofindicating and actuating fuses are made of the same insulating materialsas casings of power fuses the condition of which they are to sense.Thermoplastic materials and more particularly thermoplastic syntheticresins are generally deemed unsuitable for casings of power fusesbecause, in operation, such casings are likely to be subjected totemperatures exceeding the softening temperatures of thermoplasticsynthetic resins. I have found that thermoplastic resins are well suitedas materials for casings of indicating and actuating fuses which areseparate, and arranged remotely from, the power fuses the condition ofwhich they are to sense. This suitability of thermoplastic resins is dueto the fact that such indicating and actuating fuses are normally notcurrent carrying and, therefore, normally not subjected to i -r lossesand concomitant heat generation. It requires, however, some precautionsto be able to provide indicating and actuating fuses with casings ofsynthetic thermoplastic resins. One of these precautions or requirementsis minimizing the length of the fusible element orstriker-pin-restraining wire which is arranged inside of the casing, andanother of these precautions or requirements is the arrangement of thefusible element or ea /awe striker-pin-restraining wire coextensive withthe axis of the casing, as clearly shown in FIG. 1, where referencecharacter 3 has been applied to indicate the fusible element orstriker-pin-restraining wire. The latter is made of steel to comply withhigh tensile strength requirements. Casing 1 may be made of an extrudedthermoplastic resin as, for instance, an acrylonitrile-butadiene-styrenecopolymer having a high degree of dimensional stability.

A pair of terminal elements or terminal caps 2 is arranged adjacent theends of casing 1 and closes said ends. Each terminal element or terminalcap has a perforation 2a in the center thereof. Wire 3 is threadedthrough perforations 2a and tautly stretched along the axis of easing 1and is conductively interconnecting caps 2 as will be explained belowmore in detail. An additional pair of caps 6 and 7 is mounted on caps 2.Cap 7 defines jointly with one of caps 2 a chamber 13 for accommodatinga striker pin mechanism. The latter is arranged in coaxial relation tocasing 1 and includes a substantially cylindrical striker pin 4 having apredetermined diameter, a helical striker-pin-biasing spring and astriker pin support 14 under the bias of spring 5 and formed by a partdistinct from striker pin 4. Striker pin support 14 is preferably madeof brass. If striker pin 4 is to perform a mechanical duty involvingtransmission of a relatively high force, pin 4- is preferably made ofsteel. Striker pin support 14 defines a first relatively narrow axialpassage 15 having an entrance at the side of support 14 juxtaposed tocasing 1 and support 14 further defines a second axial passage 16 havingan entrance 17 at the side of support 14 remote from casing 1. Passage16 is equal in diameter to the diameter of striker pin 4. One end ofrestraining wire 3 is threaded through the narrow passage 15 in support14 and forms a knot 18 at the axially inner end of passage 15. Strikerpin 4 is inserted into passage 16 through the entrance 17 thereof andplugs passage 16. Both ends of striker pin 4 are preferably convex. Theend of striker pin 4 remote from casing 1 projects through a centralopening 7a in cap 7 and is slidably guided in said opening. The end ofstriker pin 4 juxtaposed to casing 1 engages knot 18 under somepressure, tending to slightly expand knot 18 and thus to prevent thesame from slipping through the narrow passage 15 in support 14 throughwhich wire 3 is threaded.

Depending upon the particular application of the device a striker pin 4aof insulating material as shown in FIG. 4 may be substituted for thestriker pin 4 of metal shown in FIG. 1. If the striker pin is of metaland intended to establish an electrical contact with some othercooperating part, the striker pin should preferably be silver plated, orsilver surfaced by any other desired silver surfacing method. Thesupport 14 for the striker pin 4 does not lend itself to silverelectroplating and does not need to be silver plated. Silver plating ofa metallic striker pin as shown in FIG. 1 is conducive to establishing agood electrical contact in such instances where the striker pincooperates with another contact not covered with an oxide or similarfilm whose conductivity is low. Applying the modification of the strikerpin 4b shown in FIG. 5 is indicated where the striker pin is intended tocooperate with a contact of copper, eg a copper bus, having an oxidefilm which is a poor conductor of electricity. According to FIG. 5 theend of striker pin 4b remote from casing 1 defines a sharp point adaptedto pierce a copper oxide layer having a small conductivity and, by sodoing, to establish a contact of low resistance in spite of the presenceof such a layer.

It will thus be apparent that the fact that pin 4 and support 14 areformed by two distinct parts imparts a great flexibility and/ oradaptability to indicating and actuating fuses embodying the presentinvention.

Referring now again to FIG. 1, an eyelet 12 is inserted into the centerperforation in the inner cap 2 at the right hand end of easing 1. Eyelet12 forms a bushing for the passage of steel wire 3 from the inside ofcasing 1 to the outside thereof. Eyelet 12 and the convex surface of thecap 2 on the right hand end of casing 1 are filled with soft solder,thus afiixing the right end of wire 3 to said cap. After wire 3 has beensoldered to the right inner cap 2 the loose end of Wire 3 is bent aroundthe top of said cap and its end cut off at point 20 after the rightouter cap 6 is fully seated. A center perforated washer 9 of fiber ispreferably arranged inside the right inner cap 2. Where it is desirableto achieve a high degree of tightness a rubber seal 21 may be insertedbetween the axially outer surface of left cap 2 and the axially innersurface of support 14. Such a seal frictionally engages wire 3 and isbeing slightly compressed between parts 14 and 2.

A pulverulent arc-quenching filler inside casing 1 may be dispensed Withas long as the circuit voltage is relatively low, i.e. in the order ofvolt. For higher circuit voltages a pulverulent arc-quenching fillermust be placed into casing 1. If casing 1 is made of thermoplasticextruded tubing the pulverulent arc-quenching filler must be compatiblewith such casing materials. Gypsum powder has been found to be acompatible pulverulent arc-quenching filler, and quartz sand has beenfound to be an incompatible pulverulent arc-quenching filler.

The structure of FIG. 1 is intended to be used in an appropriate fuseholder having spaced contact clips supporting the outer caps or ferrules6 and 7. The current path through the device is as follows: left outercap 7, left inner cap 2, support 14, wire 3, right inner cap 2, rightouter cap 6.

When restraining wire 3 is caused to carry an electric current, thougheven of relatively small magnitude, wire 3 melts, thus releasing strikerpin support 14. Now support 14 and striker pin 4 are jointly propelledby spring 5 to the left from their respective position shown in FIG. 1.

Having disclosed a preferred embodiment of my invention it is desiredthat the same be not limited to the particular structure disclosed. Itwill be obvious to any person skilled in the art that many modificationsand changes may be made without departing from the broad spirit of theinvention. Therefore it is desired that the invention be interpretedbroadly, and that it be limited only as required by the prior state ofthe art.

I claim as my invention:

1. An indicating and actuating fuse which is normally notcurrent-carrying and which becomes current-carrying upon blowing of amain fuse by which it is normally shunted, said indicating and actuatingfuse comprising a tubular casing of insulating material; a pair ofterminal caps arranged adjacent the ends of said casing and closing saidends, each of said pair of caps having a perforation in the centerthereof; a striker pin mechanism arranged in coaxial relation to andsupported by said casing, said mechanism including a striker pin ofpredetermined diameter having a smooth lateral surface, astriker-pinbiasing spring and a striker pin support under the action ofsaid spring and formed by a solid of revolution separate and distinctfrom said striker pin and support defining a first relatively narrowaxial passage having an entrance at the side ofsaid support juxtaposedto said casing and said support further defining a second axial passagehaving a smooth lateral surface and having an entrance at the side ofsaid support remote from said casing and being conical at the endthereof adjacent said casing, said second passage being equal indiameter to said predetermined diameter of said striker pin and saidsecond passage being shorter than said striker pin; astriker-pinrestraining wire of steel arranged inside said casing incoaxial relation thereto exceeding the length of said casing and tautlystretched along the axis thereof and threaded through said perforationin each of said pair of terminal caps and conductively interconnectingsaid pair of terminal caps, one end of said wire being threaded throughsaid first passage into said conical end of said second passage andaflixed in said second passage to said support; said striker pin beingaxially driven into said second passage through said entrance thereofand press-fitted into and plugging said second passage, and the end ofsaid striker pin adjacent said support directly engaging the end of saidwire inside of said second passage and clamping said end of said wireagainst the surface of said second passage.

2. An indicating and actuating fuse which is normally notcurrent-carrying and which becomes current-carrying upon blowing of amain fuse by which it is normally shunted, said indicating and actuatingfuse comprising a tubular casing of insulating material; a pair ofterminal elements arranged adjacent the ends of said casing and closingsaid ends, each of said pair of terminal elements having a perforationin the center thereof; a striker pin mechanism arranged in coaxialrelation to said casing, said mechanism including a silver surfacedstriker pin 'having a predetermined diameter, a striker-pin biasingspring and a striker pin support under the bias of said spring formed bya part distinct from said striker pin and having a bare surface, saidsupport defining a first relatively narrow axial passage having anentrance at the side of said support juxtaposed to said casing and saidsupport further defining a second axial passage having an entrance atthe side of said support remote from said casing, said secondpassagebeing equal in diameter to said predetermined diameter of said strikerpin and said second passage being shorter than said striker pin; astriker-pinrestraining wire of steel inside of said casing exceeding thelength of said casing and tautly stretched along the axis thereof andthreaded through said perforation in each of said pair of terminalelements and conductively interconnecting said pair of terminalelements, one end of said wire being threaded through said first passageand forming a knot at the axially inner end of said first passage; andsaid striker pin being inserted into said second passage through saidentrance thereof and plugging said second passage.

3. An indicating and actuating fuse which is normally notcurrent-carrying and which becomes current-carrying upon blowing of amain fuse by which it is normally shunted, said indicating and actuatingfuse comprising a tubular casing of insulating material; a pair ofterminal caps each mounted on one of the ends of said casing and closingsaid ends, each of said pair of caps having a perforation in the centerthereof; a striker pin mechanism arranged in coaxial relation to saidcasing and including a cylindrical striker pin having a predetermineddiameter, a smooth lateral surface and being semispherical at least atone end thereof, a striker-pin-biasing spring and a striker pin supportunder the bias of said spring and formed by a part distinct from saidstriker pin, said support defining a first relatively narrow axialpassage having an entrance at the side thereof juxtaposed to said casingand said support further defining a second axial passage having anentrance at the side thereof remote from said casing and being smooth atthe lateral sides thereof and conical at the end thereof adjacent tosaid casing, said second passage being equal in diameter to saidpredetermined diameter of said striker pin and said second passage beingshorter than said striker pin; a striker-pin-restraining wire of steelinside said casing tautly stretched along the axis thereof and threadedthrough said perforation in each of said pair of caps and conductivelyinterconnecting said pair of caps, one end of said wire being threadedthrough said first passage and forming a knot at said conical end ofsaid second passage, and said striker pin being pressfitted into saidentrance of said second passage plugging said second passage andengaging said knot under pressure with a semispherical end, thereof andthereby compressing said knot. 4. An indicating and actuating fuse whichis normally not current-carrying and which becomes current-carrying uponblowing of a main fuse .by which it is normally shunted, said indicatingand actuating fuse comprising a tubular casing of insulating material; apair of terminal caps arranged adjacent the ends of said casing andclosing said ends, each of said pair of terminal caps having aperforation in the center thereof; a striker pin mechanism arranged incoaxial relation to said casing, said mechanism including a cylindricalstriker pin of insulating material having a predetermined diameter and asmooth lateral surface, a striker pin biasing spring and a metallicstriker pin support under the bias of said spring, said support defininga first relatively narrow axial passage having an entrance at the sideof said support juxtaposed to said casing and said support furtherdefining a second axial cylindrical passage having a smooth lateralsurface, an entrance at the side of said support remote from said casingand a conical end adjacent said casing, said second passage being equalin diameter to said predetermined diameter of said striker pin and saidsecond passage being shorter than said striker pin; astriker-pin-restraining wire of steel inside said casing tautlystretched along the axis thereof and threaded through said perforationin each of said pair of terminal elements and conductivelyinterconnecting said pair of terminal elements, one end of said wirebeing threaded through said first passage and forming a knot at saidconical end of said second passage, and said striker pin beingpressfitted into said second passage through said entrance thereof andplugging said second passage.

References Cited by the Examiner UNITED STATES PATENTS 2,026,381 12/35Fiedler 200121 2,794,095 5/57 Kozacka 200l21 2,794,096 5/57 Kozacka200121 2,854,549 9/58 Duerkob 200-121 3,010,000 11/61 Swain et a1200-13l 3,094,600 6/63 Kozacka 200-432 I FOREIGN PATENTS 724,830 11/43Germany.

BERNARD A. GILHEANY, Primary Examiner.

1. AN INDICATING AND ACTUATING FUSE WHICH IS NORMALLY NOTCURRENT-CARRYING AND WHICH BECOMES CURRENT-CARRYING UPON BLOWING OF AMAIN FUSE BY WHICH IT IS NORMALLY SHUNTED, SAID INDICATING AND ACTUATINGFUSE COMPRISING A TUBULAR CASING OF INSULATING MATERIAL; A PAIR OFTERMINAL CAPS ARRANGED ADJACENT THE ENDS OF SAID CASING AND CLOSING SAIDENDS, EACH OF SAID PAIR OF CAPS HAVING A PERFORATION IN THE CENTERTHEREOF; A STRIKER PIN MECHANISM ARRANGED IN COAXIAL RELATION TO ANDSUPPORTED BY SAID CASING, SAID MECHANISM INCLUDING A STRIKER PIN OFPREDETERMINED DIAMETER HAVING A SMOOTH LATERAL SURFACE, ASTRIKER-PINBIASING SPRING AND A STRIKER PIN SUPPORT UNDER THE ACTION OFSAID SPRING AND FORMED BY A SOLID FOR REVOLUTION SEPARATE AND DISTINCTFROM SAID STRIKER PIN AND SUPPORT DEFINING A FIRST RELATIVELY NARROWAXIAL PASSAGE HAVING AN ENTRANCE AT THE SIDE OF SAID SUPPORT JUXTAPOSEDTO SAID CASING AND SAID SUPPORT FURTHER DEFINING A SECOND AXIAL PASSAGEHAVING A SMOOTH LATERAL SURFACE AND HAVING AN ENTRANCE AT THE SIDE OFSAID SUPPORT REMOTE FROM SAID CASING AND BEING CONICAL AT THE ENDTHEREOF ADJACENT SAID CASING, SAID SECOND PASSAGE BEING EQUAL INDIAMETER TO SAID PREDETERMINED DIAMETER OF SAID STRIKER PIN AND SAIDSECOND PASSAGE BEING SHORTER THAN SAID STRIKER PIN; ASTRIKER-PINRESTRAINING WIRE OF STEEL ARRANGED INSIDE SAID CASING INCOAXIAL RELATION THERETO EXCEEDING THE LENGTH OF SAID CASING AND TAUTLYSTRETCHED ALONG THE AXIS THEREOF AND THREADED THROUGH SAID PERFORATIONIN EACH OF SAID PAIR OF TERMINAL